Karl Walli worked at the IRS from 1986 to 1996. An original member of the Financial Institutions & Products division of Chief Counsel, he specialized in the taxation of derivatives and was one of the principal authors of the notional principal contract regulations. After transferring to the International Division in 1991, Karl worked on a variety of banking and financial product issues, including foreign currency, subpart F, and interest expense allocation. He joined the Washington, D.C. office of Weil Gotshal & Manges in 1996, where he was a partner in the tax department since 2000 advising clients on inbound and outbound issues including the application of U.S. tax rules to derivative financial instruments, capital market transactions, and effectively connected income. He returned to the government in September, 2009, joining the Treasury Department as Senior Counsel (Financial Products).